1. Field of the Invention
This invention relates to a so-called low noise radial tire having an improved cornering stability which can largely reduce noise level without damaging the cornering stability of the tire and the braking performance on a wet road surface.
2. Related Art Statement
Recently, noise generated from automobiles has become a great social problem and particularly, automobile noise becomes regulated by a law, so that it is urgently needed to reduce the noise level. On the other hand, it is required to ensure a low noise level inside the automobile from a viewpoint of the enhancement in the automobile riding environment. In any case, the demand on the reduction of noise becomes indispensable.
Heretofore, it has been said that the noise of the radial tire is effectively reduced by the improvement of tread pattern, unharmonization of pattern pitch or the like. However, such a change of the tread pattern largely affects the braking performances on wet road surface and the like, so that the freedom degree of such a change is very small in view of the safety and is greatly restricted.
Therefore, it is desired to establish a technique capable of reducing the noise without changing the tread pattern but effective countermeasures have not yet been found.
The inventors have made various studies in order to obtain low noise tires and considered to require an approach different from the conventional technique because there was observed the conflicting phenomenon that the braking performance on a wet road surface is reduced by changing the tread pattern as previously mentioned. Consequently, the inventors have made various attempts on the design factors of various tires, but the reduction of noise level was about 1 decibel at most by these attempts.
On the other hand, the inventors noticed that the noise is reduced by about 0.3 decibel in the conventional tire of aramid fold belt structure consisting of a combination of steel cord layer and folded aramid fiber cord layer. The inventors made further studies with respect to this belt structure and found that the noise can largely be reduced by interposing an organic fiber cord layer having given properties between steel cord layer and tread rubber, which has been filed as U.S. patent application Ser. No. 927,016.
In this case, however, the belt layer of organic fiber cord other than aramid fiber cord is used instead of the steel cord belt layer, so that there is no great difference in the feeling of actual running performances, but it is frequently evaluated that the tire rigidity, particularly limit cornering property due to the shortage of belt rigidity, the steering property of handle and the like are still poor. As a result, it is considered that such a tire is necessary to be further improved.